Polymer and preparation method thereof, negative electrode material, negative electrode sheet, and lithium-ion battery

Abstract

The present application discloses a polymer and its preparation method, negative electrode material, negative electrode plate, and lithium-ion battery, belonging to the field of electrode materials. The polymer includes: at least one first repeating unit and an optional second repeating unit, the first repeating unit includes: an aromatic dianhydride residue containing an ether bond and a diamine residue with an aliphatic cyclic structure, the anhydride group in the aromatic dianhydride residue containing an ether bond is connected to the amine group in the diamine residue with an aliphatic cyclic structure; the second repeating unit includes: an aromatic dianhydride residue containing an ether bond and a diamine residue with a polar functional group, the anhydride group in the aromatic dianhydride residue containing an ether bond is connected to the amine group in the diamine residue with a polar functional group. The polymer has a significant inhibitory effect on the volume expansion of silicon-based negative electrode materials and will significantly improve the first efficiency and cycle stability of lithium-ion batteries.

Description

Technical Field

[0001] The present disclosure relates to the field of electrode materials, and in particular to polymers and preparation methods thereof, negative electrode materials, negative electrode sheets, and lithium-ion batteries. Background Art

[0002] Silicon has a theoretical specific capacity of up to 4200 mAh / g, and silicon-based anode materials are of great significance for the development of high-energy-density lithium-ion batteries. However, silicon-based anode materials have a large volume expansion coefficient. During the lithiation / delithiation process, the volume of silicon-based anode materials changes by as much as 300%. This causes the silicon-based anode materials to pulverize and shatter during the charge and discharge cycles due to this volume change, which restricts the capacity, coulombic efficiency, and cycle stability of lithium-ion batteries.

[0003] The related technology mixes polyimide binder, silicon-based negative electrode material and conductive agent, and uses polyimide binder to curb the cracking and crushing caused by volume expansion of silicon-based negative electrode material during charge and discharge cycles.

[0004] However, the polyimide binder provided by the related art has at least the following technical problems: it has limited effect in inhibiting the volume expansion of silicon-based negative electrode materials, which will reduce the initial coulombic efficiency and cycle stability of lithium-ion batteries. Summary of the Invention

[0005] In view of this, the present disclosure provides a polymer and a preparation method thereof, a negative electrode material, a negative electrode plate, and a lithium-ion battery, which can solve the above technical problems.

[0006] Specifically, the following technical solutions are included:

[0007] In one aspect, a polymer is provided, comprising: at least one first repeating unit and an optional second repeating unit, wherein the first repeating unit comprises: an aromatic dianhydride residue containing an ether bond and a diamine residue having an alicyclic structure, wherein the anhydride group of the aromatic dianhydride residue containing an ether bond is linked to the amine group of the diamine residue having an alicyclic structure;

[0008] The second repeating unit includes an aromatic dianhydride residue containing an ether bond and a diamine residue having a polar functional group, wherein the anhydride group in the aromatic dianhydride residue containing an ether bond is connected to the amine group in the diamine residue having a polar functional group.

[0009] The polymer provided by the embodiments of the present disclosure contains the following groups in its molecule: (1) an aromatic dianhydride residue containing an ether bond, (2) a diamine residue having an alicyclic structure, and optionally (3) a diamine residue having a polar functional group. The aromatic dianhydride residue (1) containing an ether bond can enhance the molecular mobility of the polymer, making the polymer readily soluble in polar solvents such as N-methylpyrrolidone at room temperature, facilitating application without the need for subsequent heat treatment, and significantly reducing processing difficulty. For (2) diamine residues with aliphatic ring structures, this group is a saturated structure, which can reduce the proportion of conjugated units contained in the polymer main chain, inhibit the formation of charge transfer complexes, and thus reduce the side reaction between polyetherimide and lithium ions; for (3) diamine residues with polar functional groups, the polar functional groups can connect the polymer with functional groups such as hydroxyl groups on the silicon surface through hydrogen bonds or chemical bonds, thereby improving the adhesion. At the same time, the polar functional groups can also improve the adhesion between the polymer and the carbon material and the current collector, and promote the formation of the negative electrode solid electrolyte interface (SEI) film. It can be seen that the presence of the above groups in the polymer greatly improves the expansion and cycle performance of the silicon-based negative electrode.

[0010] The polymer provided in the embodiments of the present disclosure can be used as a binder to prepare a negative electrode sheet, and then used in a lithium-ion battery, and has at least the following advantages:

[0011] (1) The polymers provided in the embodiments of the present disclosure have improved solvent solubility and melt fluidity, with a solubility of more than 20% in polar solvents such as N-methylpyrrolidone at room temperature. When the polymers provided in the embodiments of the present disclosure are used to prepare negative electrode plates, no additional high-temperature or chemical treatment steps are required, which not only significantly reduces the processing difficulty but also avoids the problem of negative electrode plate performance degradation caused by oxidation of the silicon active material or current collector due to high-temperature post-treatment.

[0012] (2) Compared with the wholly aromatic polyimide or wholly aromatic polyetherimide provided by the related art, the polymer provided by the embodiment of the present disclosure is based on its diamine residue with an aliphatic cyclic structure, which reduces the use of aromatic groups and can effectively inhibit the formation of charge transfer complexes within or between polymer molecules, reduce the side reaction between polyetherimide and lithium ions, and thus reduce the consumption of active lithium, which is beneficial to improving the coulombic efficiency and first efficiency of lithium-ion batteries.

[0013] (3) The polymer provided in the embodiments of the present disclosure is based on its diamine residue with polar functional groups, which can effectively enhance the bonding strength between the polymer and the silicon-based negative electrode material and the current collector, making the negative electrode plate less likely to crack and pulverize during the charging and discharging process, which is beneficial for the lithium-ion battery to maintain sufficient capacity and have stronger cycle stability.

[0014] (4) The polymer with the above chemical structure provided by the embodiments of the present disclosure has high elastic modulus, good toughness and high mechanical strength. Thus, when it is used as a binder to prepare a negative electrode sheet, even if the negative electrode sheet contains a higher silicon content, it can inhibit the volume expansion of the silicon-based negative electrode material and prevent peeling and disintegration at the interface between the silicon-based negative electrode material and the conductive agent and current collector during charge and discharge, thereby maintaining the structural stability of the negative electrode sheet, which is beneficial to keeping the lithium-ion battery with sufficient capacity and having stronger cycle stability.

[0015] In some possible implementation manners, the aromatic dianhydride residue containing an ether bond includes: a divalent group with an aromatic structure, two ether bonds, and two phthalic anhydride residues, and two end groups of the divalent group with an aromatic structure are respectively connected to the phenyl group of one phthalic anhydride residue through one of the ether bonds.

[0016] That is to say, the chemical structural formula of the polymer provided by the embodiments of the present disclosure is as follows:

[0017]

[0018] Wherein, is a divalent group with an aromatic structure;

[0019] R 1 is a diamine residue with an alicyclic structure;

[0020] R 2 is a diamine residue with a polar functional group.

[0021] Wherein, for this group is the above-mentioned aromatic dianhydride residue containing an ether bond.

[0022] In some possible implementation manners, both m and n are integers, 0 < m < 500, 0 ≤ n < 100, and n / m ≤ 1 / 4. Wherein, the numerical ranges of m and n are defined as above, which can make the molecular weight of the polymer within the desired range to obtain a suitable viscosity; and making n / m ≤ 1 / 4 to increase the amount of the diamine residue with an alicyclic structure, thereby reducing the side reaction with lithium ions.

[0023] In some possible implementation manners, the divalent group with an aromatic structure includes: a first phenyl group and an optional third repeating unit, and the third repeating unit includes: a linking group and a second phenyl group;

[0024] The first phenyl group is connected to one end group of the linking group in the third repeating unit, and the second phenyl group is connected to the other end group of the linking group;

[0025] The first phenyl group and the second phenyl group are substituted or unsubstituted;

[0026] The connecting group is a single bond, -O-, -S-, -S(O)-, -SO2-, -C(O)- or a C1-18 organic bridging group.

[0027] In some possible implementations, the first phenyl group has a first substituent, and the first substituent is a halogen atom or a monovalent C1-10 alkyl group;

[0028] The second phenyl group has a second substituent, and the second substituent is a halogen atom or a monovalent C1-10 alkyl group;

[0029] The number of the first substituent and the number of the second substituent are both 1-4.

[0030] In some possible implementations, the number of the third repeating units is 0-4.

[0031] Based on the above, it can be seen that the divalent group with an aromatic structure The chemical structure is shown below:

[0032]

[0033] Among them, R a and R b Each independently is a halogen atom or a monovalent C 1-10 Alkyl group, wherein the monovalent C 1-10 The alkyl group refers to a saturated aliphatic group containing 1 to 10 carbon atoms, including straight-chain alkyl and branched-chain alkyl, for example, methyl, ethyl, propyl, butyl, etc. a and R b It can be the same or different.

[0034] X a is a single bond, -O-, -S-, -S(O)-, -SO2-, -C(O)- or C 1-18 Organic bridging group, wherein the C 1-18 The organic bridging group refers to a bridging group containing 1 to 18 carbon atoms. 1-18 The organic bridging group may be cyclic or acyclic, or the C 1-18 The organic bridging group may be aromatic or non-aromatic. 1-18 The organic bridging group may further contain heteroatoms, for example, the heteroatoms include but are not limited to halogen atoms, oxygen atoms, nitrogen atoms, sulfur atoms or fluorine atoms.

[0035] p, q and c are each independently an integer of 0-4, wherein p, q and c may be the same, different, or partially the same, and p, q and c are not 0 at the same time.

[0036] In some possible implementations, the diamine residue having an aliphatic ring structure is derived from at least one of the following aliphatic ring-containing diamine monomer compounds: 1,2-cyclohexanediamine, 1,3-cyclohexanediamine, 4-methyl-1,3-cyclohexanediamine, 1,4-cyclohexanediamine, trans-1,4-cyclohexanediamine, cis-1,4-cyclohexanediamine, 1,4-diaminomethylcyclohexane, 1,3-diaminomethylcyclohexane, bis(aminomethyl)norbornane, isophoronediamine, adamantane-1,3-diamine, 2,2'-bis(trifluoromethyl)-4,4'-diamino-chain cyclohexane, 4,4'-methylenebis(cyclohexylamine), 4,4'-methylenebis(2-methylcyclohexylamine), 2,2'-bis(4-aminocyclohexyl)hexafluoropropane, and 1,1'-diadamantane-3,3'-diamine.

[0037] The diamine residue with an aliphatic ring structure provided by the above-mentioned aliphatic ring-containing diamine monomer can effectively inhibit the formation of charge transfer complexes within or between polymer molecules, reduce the side reaction between polyetherimide and lithium ions, and thus reduce the consumption of active lithium, which is beneficial to improving the coulombic efficiency and first efficiency of lithium-ion batteries.

[0038] In some possible implementations, the polar functional group is selected from at least one of a carboxyl group, a hydroxyl group, and a sulfonic acid group.

[0039] In some possible implementations, the diamine residue having a polar functional group is derived from at least one of the following diamine monomer compounds containing polar groups: 3,5-diaminocyclohexanecarboxylic acid, 3,5-diaminobenzoic acid, 4,4'-diaminobiphenyl-2,2'-dicarboxylic acid, 5,5'-methylenebis(2-aminobenzoic acid), 3,3'-dihydroxybenzidine, 2,2'-bis(3-amino-4-hydroxyphenyl)propane, 2,2'-bis(3-amino-4-hydroxyphenyl)propane, -4-hydroxyphenyl)hexafluoropropane, bis(3-amino-4-hydroxyphenyl) sulfone, 4,6-diaminoresorcinol dihydrochloride, 2,5-diamino-1,4-benzenedithiol dihydrochloride, 2,6-dihydroxy-3,7-diaminotridisolene, 2,2'-bis[3-(4-aminobenzamido)-4-hydroxyphenyl]hexafluoropropane, 4,4'-diamino-2,2'-biphenyldisulfonic acid, 4,4'-diaminostilbene-2,2'-disulfonic acid.

[0040] The diamine residues with polar functional groups provided by the above diamine monomers containing polar groups can effectively increase the adhesion between the polymer and the silicon-based anode material, carbon material, and current collector, making the anode electrode sheet不易 to crack and pulverize during charge and discharge, ensuring that the lithium-ion battery maintains sufficient capacity and has stronger cycle stability.

[0041] On the other hand, a method for preparing a polymer is provided. The polymer is as shown in any of the above, and the method for preparing the polymer includes:

[0042] Under an inert atmosphere and the action of a catalyst, a dianhydride monomer, a diamine monomer containing an alicyclic ring, and an optional diamine monomer containing a polar group are subjected to a polymerization reaction in a first solvent to obtain the polymer.

[0043] In some examples, the chemical structural formula of the polymer involved above is as follows:

[0044]

[0045] Among them, is a divalent group with an aromatic structure;

[0046] R 1 is a diamine residue with an alicyclic ring structure;

[0047] R 2 is a diamine residue with a polar functional group;

[0048] Both m and n are integers, 0 < m <, 0 ≤ n < 100, and n / m ≤ 1 / 4.

[0049] In some possible implementation manners, the dianhydride monomer includes: a divalent group with an aromatic structure, two ether bonds, and two phthalic anhydride groups;

[0050] The two end groups of the divalent group with an aromatic structure are respectively connected to the phenyl group of one phthalic anhydride group through one of the ether bonds.

[0051] Based on the above, the chemical structural formula of the dianhydride monomer is as follows:

[0052]

[0053] R 1 is a diamine residue with an alicyclic ring structure, that is, the group remaining in the polymer after the diamine monomer containing an alicyclic ring undergoes a polymerization reaction.

[0054] R 2 is a diamine residue with a polar functional group, that is, the group remaining in the polymer after the diamine monomer containing a polar group undergoes a polymerization reaction.

[0055] In some possible implementations, the divalent group having an aromatic structure includes: a first phenyl group and an optional third repeating unit, and the third repeating unit includes: a linking group and a second phenyl group;

[0056] The first phenyl group is connected to the first end group of the linking group in the third repeating unit, and the second phenyl group is connected to the second end group of the linking group;

[0057] The first phenyl group and the second phenyl group are substituted or unsubstituted;

[0058] The connecting group is a single bond, -O-, -S-, -S(O)-, -SO2-, -C(O)- or C 1-18 organic bridging group;

[0059] The number of the third repeating unit is 0-4.

[0060] In some possible implementations, the first phenyl group has a first substituent, and the first substituent is a halogen atom or a monovalent C 1-10 alkyl groups;

[0061] The second phenyl group has a second substituent, and the second substituent is a halogen atom or a monovalent C 1-10 alkyl groups;

[0062] The number of the first substituent and the number of the second substituent are both 1-4.

[0063] In some possible implementations, the aliphatic ring-containing diamine monomer is selected from at least one of the following compounds: 1,2-cyclohexanediamine, 1,3-cyclohexanediamine, 4-methyl-1,3-cyclohexanediamine, 1,4-cyclohexanediamine, trans-1,4-cyclohexanediamine, cis-1,4-cyclohexanediamine, 1,4-diaminomethylcyclohexane, 1,3-diaminomethylcyclohexane, bis(aminomethyl)norbornane, isophoronediamine, adamantane-1,3-diamine, 2,2'-bis(trifluoromethyl)-4,4'-diamino-chain cyclohexane, 4,4'-methylenebis(cyclohexylamine), 4,4'-methylenebis(2-methylcyclohexylamine), 2,2'-bis(4-aminocyclohexyl)hexafluoropropane, and 1,1'-diadamantane-3,3'-diamine.

[0064] In some possible implementations, the polar group-containing diamine monomer is selected from at least one of the following compounds: 3,5-diaminocyclohexanecarboxylic acid, 3,5-diaminobenzoic acid, 4,4'-diaminobiphenyl-2,2'-dicarboxylic acid, 5,5'-methylenebis(2-aminobenzoic acid), 3,3'-dihydroxybenzidine, 2,2'-bis(3-amino-4-hydroxyphenyl)propane, 2,2'-bis(3-amino-4-hydroxyphenyl)hexafluoropropane, bis(3-amino-4-hydroxyphenyl)sulfone, 4,6-diaminoresorcinol dihydrochloride, 2,5-diamino-1,4-benzenedithiol dihydrochloride, 2,6-dihydroxy-3,7-diaminotrisole, and 2,2'-bis[3-(4-aminobenzamido)-4-hydroxyphenyl]hexafluoropropane.

[0065] In some possible implementations, the first solvent includes at least one of a phenolic solvent, a polyhalogenated benzene solvent, N,N-dimethylacetamide, N-methyl-2-pyrrolidone, nitrobenzene, and benzonitrile.

[0066] The first solvent can not only dissolve the dianhydride monomer, the aliphatic ring-containing diamine monomer, and the polar group-containing diamine monomer, but also has a smaller chain transfer constant, which is beneficial for the polymerization reaction to proceed fully and thoroughly, and the polymerization reaction is faster.

[0067] In some possible implementations, the catalyst includes at least one of isoquinoline, triethylamine, benzoic acid, and p-hydroxybenzoic acid. Under the catalytic action of the above catalyst, the polymerization reaction can be initiated quickly and effectively.

[0068] Illustratively, the polymerization reaction of the dianhydride monomer, the aliphatic ring-containing diamine monomer, and the optional polar group-containing diamine monomer in a first solvent under an inert atmosphere and a catalyst comprises:

[0069] uniformly mixing the dianhydride monomer, the aliphatic ring-containing diamine monomer, and optionally the polar group-containing diamine monomer with the first solvent to obtain a first mixed solution;

[0070] uniformly mixing the first mixed liquid and the catalyst at a first set temperature to obtain a second mixed liquid;

[0071] allowing the second mixed liquid to undergo the polymerization reaction at a second set temperature to obtain a reaction product solution containing a polymer;

[0072] The polymer-containing reaction product solution is subjected to separation treatment to obtain the polymer.

[0073] In some possible implementations, the first set temperature is 75°C-90°C. Within this temperature range, the dianhydride monomer, the aliphatic ring-containing diamine monomer, the polar group-containing diamine monomer and the catalyst can be fully dissolved in the first solvent to form a second mixed liquid with a uniform texture.

[0074] The second set temperature is 160° C.-200° C. Within this temperature range, the polymerization reaction can proceed sufficiently, thoroughly, rapidly and controllably, so as to facilitate obtaining a polymer with a desired molecular weight.

[0075] Illustratively, the solid content of the first mixed liquid is 20 wt%-40 wt%.

[0076] Exemplarily, the separation treatment of the polymer-containing reaction product solution includes:

[0077] uniformly mixing the polymer-containing reaction product solution with a second solvent to obtain a third mixed solution having a solid content of 3 wt % to 7 wt %;

[0078] Using the precipitate to precipitate the third mixed solution to obtain a first solid reaction product;

[0079] extracting the solid reaction product with an extracting solution to obtain a second solid reaction product;

[0080] The second solid reaction product is dried to obtain the polyetherimide.

[0081] In some possible implementations, the second solvent includes at least one of a phenolic solvent, a polyhalogenated benzene solvent, N,N-dimethylacetamide, N-methyl-2-pyrrolidone, nitrobenzene, and benzonitrile.

[0082] In another aspect, a negative electrode material is provided, the negative electrode material comprising: a binder, an active material, and a conductive agent;

[0083] Wherein, the binder includes any one of the polymers described above in the embodiments of the present disclosure;

[0084] The active material includes a silicon-based negative electrode material.

[0085] In some possible implementations, the active material further includes a carbon-based negative electrode material;

[0086] The weight percentage of the silicon-based negative electrode material in the active material is 1 wt % to 99.5 wt %.

[0087] Exemplarily, the silicon-based negative electrode material includes at least one of silicon, silicon-oxygen material, and silicon-carbon material;

[0088] The carbon-based negative electrode material includes at least one of graphite, hard carbon, and soft carbon.

[0089] In some possible implementations, the weight percentage of the binder in the negative electrode material is 1 wt%-20 wt%;

[0090] The weight percentage of the conductive agent in the negative electrode material is 1wt%-20wt%;

[0091] The active material is the balance.

[0092] The polymer, within the above weight percentage range, can ensure adhesion and inhibit expansion of the silicon active material, while reducing the internal resistance of the negative electrode sheet and increasing the proportion of the silicon-based negative electrode material.

[0093] In some examples, the conductive agent includes, but is not limited to, at least one of conductive graphite, conductive carbon black, acetylene black, carbon nanotubes, and graphene. Using such conductive agents can reduce the impedance of the negative electrode and improve rate performance.

[0094] The active material is the balance, that is, the amount of the active material is such that the total weight percentage of the polymer, the active material, and the conductive agent is 100%.

[0095] In another aspect, a negative electrode plate is provided, comprising: an active material layer and a current collector, wherein the active material layer is located on at least one surface of the current collector;

[0096] The active material layer is prepared by using any of the negative electrode materials described above in the embodiments of the present disclosure.

[0097] Illustratively, the preparation method of the negative electrode plate is as follows: dissolving a polymer in a polar solvent to obtain a glue solution; mixing the glue solution with an active material and a conductive agent, and stirring evenly to obtain a negative electrode slurry; coating the negative electrode slurry on two opposite surfaces of a current collector, and sequentially drying and rolling treatment to obtain a negative electrode plate.

[0098] When the polymer provided in the embodiments of the present disclosure is used as a binder to prepare negative electrode plates, no additional high-temperature or chemical treatment steps are required, and only simple coating and drying treatments are required. This not only significantly reduces the processing difficulty of the negative electrode plates, but also effectively avoids the problem of negative electrode plate performance degradation caused by oxidation of silicon active materials or current collectors due to high-temperature post-treatment.

[0099] In some possible implementations, the current collector includes at least one of copper foil, copper mesh, carbon-coated copper foil, stainless steel foil, stainless steel mesh, carbon-coated stainless steel foil, and nickel foil.

[0100] In some possible implementations, the current collector is obtained by calendering processing. For example, the copper foil is a rolled copper foil, and the stainless steel foil is a rolled stainless steel foil. The use of rolled copper foil and stainless steel foil with higher tensile strength can effectively avoid the problem of electrode extension caused by the expansion of the active material, and ensure the structural stability of the negative electrode during the charge and discharge cycle.

[0101] On the other hand, a lithium-ion battery is provided, which includes any one of the negative electrode plates described above in the embodiments of the present disclosure.

[0102] In addition to the above-mentioned negative electrode plate, the lithium-ion battery also includes a positive electrode plate, an electrolyte, a separator, and an encapsulation layer, wherein the electrolyte is filled in the space between the negative electrode plate and the positive electrode plate, and the separator is located in the electrolyte to isolate the negative electrode plate from the positive electrode plate.

[0103] Lithium-ion batteries store and release energy through the intercalation and deintercalation of lithium ions between the negative and positive electrodes. The electrolyte is the carrier for the transmission of lithium ions between the negative and positive electrodes. The diaphragm is ion conductive but electronically insulating. The diaphragm is used to ensure the migration of lithium ions while separating the negative and positive electrodes to prevent short circuits. BRIEF DESCRIPTION OF THE DRAWINGS

[0104] Figure 1 A schematic structural diagram of an exemplary lithium-ion battery provided in an embodiment of the present disclosure, wherein: Figure 1 The lithium ion migration state of a lithium ion battery in a charging state is illustrated;

[0105] Figure 2 This is an optical microscope 3D photograph of the negative electrode sheet based on Example 2 provided in the present disclosure after 50 cycles;

[0106] Figure 3 This is an optical microscope 3D photograph of the negative electrode sheet based on Comparative Example 2 provided in an embodiment of the present disclosure obtained after 50 cycles.

[0107] The reference numerals represent:

[0108] 100-negative electrode,

[0109] 200-positive electrode,

[0110] 300-electrolyte,

[0111] 400-diaphragm,

[0112] 500-encapsulation layer. DETAILED DESCRIPTION

[0113] To make the technical solutions and advantages of the present disclosure more clear, the embodiments of the present disclosure will be described in further detail below with reference to the accompanying drawings.

[0114] Silicon has a theoretical specific capacity of up to 4200 mAh / g. Silicon-based anode materials, such as silicon-carbon materials, silicon-oxygen materials, or pure silicon materials, are of great significance for the development of high-energy-density lithium-ion batteries. However, silicon-based anode materials have a large volume expansion coefficient. During the lithiation / delithiation process, the volume of silicon-based anode materials changes by as much as 300%. This causes the silicon-based anode materials to pulverize and shatter during the charge and discharge cycle due to this volume change, which restricts the capacity, coulombic efficiency, and cycle stability of lithium-ion batteries.

[0115] Related technologies combine a polymer binder, a silicon-based negative electrode material, and a conductive agent, using the polymer binder to prevent cracking and pulverization of the silicon-based negative electrode material caused by volume expansion during charge and discharge cycles. For example, the polymer binder is a polyimide binder, including: a fully aromatic polyimide, a polyimide precursor containing tetracarboxylic acid residues and diamine residues and / or a polyimide, or a polyimide obtained by the polymerization reaction of a diamine monomer and a dianhydride monomer.

[0116] As for wholly aromatic polyimide, there is a side reaction between wholly aromatic polyimide and lithium ions. Therefore, when it is used for a negative electrode, the first coulombic efficiency (first efficiency) of the prepared lithium-ion battery is low.

[0117] For polyimide precursors and / or polyimides containing tetracarboxylic acid residues and diamine residues, the polyimide needs to undergo a high-temperature or chemical heat treatment process when making negative electrode sheets. This not only complicates the production process of the negative electrode sheets, but also the high temperature or chemical treatment will cause oxidation of the silicon active material or the current collector, thereby resulting in a decrease in the performance of the negative electrode sheets.

[0118] Polyimide obtained by the polymerization reaction of diamine monomers and dianhydride monomers has low mechanical strength, which cannot suppress the volume expansion of the negative electrode plate under high silicon content, which is not conducive to the capacity and cycle stability of lithium-ion batteries.

[0119] According to one aspect of the embodiments of the present disclosure, a polymer is provided, comprising: at least one first repeating unit and an optional second repeating unit, wherein the first repeating unit comprises: an aromatic dianhydride residue containing an ether bond and a diamine residue having an alicyclic structure, wherein the anhydride group of the aromatic dianhydride residue containing an ether bond is linked to the amine group of the diamine residue having an alicyclic structure. The second repeating unit comprises: an aromatic dianhydride residue containing an ether bond and a diamine residue having a polar functional group, wherein the anhydride group of the aromatic dianhydride residue containing an ether bond is linked to the amine group of the diamine residue having a polar functional group.

[0120] When the polymer includes the second repeating unit, the diamine residue having an alicyclic structure in the first repeating unit and the N in the aromatic dianhydride residue containing an ether bond in the second repeating unit are connected through a single bond.

[0121] The polymer provided by the embodiments of the present disclosure contains the following groups in its molecule: (1) an aromatic dianhydride residue containing an ether bond, (2) a diamine residue having an alicyclic structure, and optionally (3) a diamine residue having a polar functional group. The aromatic dianhydride residue (1) containing an ether bond can enhance the molecular mobility of the polymer, making the polymer readily soluble in polar solvents such as N-methylpyrrolidone at room temperature, facilitating application without the need for subsequent heat treatment, and significantly reducing processing difficulty. For (2) diamine residues with aliphatic ring structures, this group is a saturated structure, which can reduce the proportion of conjugated units contained in the polymer main chain, inhibit the formation of charge transfer complexes, and thus reduce the side reaction between polyetherimide and lithium ions; for (3) diamine residues with polar functional groups, the polar functional groups can connect the polymer with functional groups such as hydroxyl groups on the silicon surface through hydrogen bonds or chemical bonds, thereby improving the adhesion. At the same time, the polar functional groups can also improve the adhesion between the polymer and the carbon material and the current collector, and promote the formation of the negative electrode solid electrolyte interface (SEI) film. It can be seen that the presence of the above groups in the polymer greatly improves the expansion and cycle performance of the silicon-based negative electrode.

[0122] The polymer provided in the embodiments of the present disclosure can be used as a binder to prepare a negative electrode sheet, and then used in a lithium-ion battery, and has at least the following advantages:

[0123] (1) The polymer provided in the embodiments of the present disclosure has better solvent solubility and melt fluidity, and has a solubility of more than 20% in polar solvents such as N-methylpyrrolidone (for example, 20% here means that 20g of polymer can be dissolved in 80g of N-methylpyrrolidone). When the polymer provided in the embodiments of the present disclosure is used to prepare the negative electrode, no additional high temperature or chemical treatment steps are required, which not only significantly reduces the processing difficulty, but also avoids the problem of negative electrode performance degradation caused by oxidation of the silicon active material or current collector due to high temperature post-treatment.

[0124] (2) Compared with the wholly aromatic polyimide or wholly aromatic polyetherimide provided by the related art, the polymer provided by the embodiment of the present disclosure is based on its diamine residue with an aliphatic cyclic structure, which reduces the use of aromatic groups and can effectively inhibit the formation of charge transfer complexes within or between polymer molecules, reduce the side reaction between polyetherimide and lithium ions, and thus reduce the consumption of active lithium, which is beneficial to improving the coulombic efficiency and first efficiency of lithium-ion batteries.

[0125] (3) The polymer provided by the embodiments of the present disclosure can effectively enhance the adhesion strength between the polymer and the silicon-based anode material and the current collector based on its diamine residues with polar functional groups, so that the prepared anode electrode sheet is not prone to cracking and pulverization during charge and discharge, which is beneficial to maintaining sufficient capacity of the lithium-ion battery and having stronger cycle stability.

[0126] (4) The polymer provided by the embodiments of the present disclosure has a high elastic modulus, good toughness and high mechanical strength. Thus, when it is used as a binder to prepare an anode electrode sheet, even if the anode electrode sheet contains a higher silicon content, it can inhibit the volume expansion of the silicon-based anode material and prevent peeling and collapse at the interface with the conductive agent and the current collector due to the volume change of the silicon-based anode material during charge and discharge, thereby maintaining the structural stability of the anode electrode sheet, which is beneficial to maintaining sufficient capacity of the lithium-ion battery and having stronger cycle stability.

[0127] In some possible implementation manners, the aromatic dianhydride residue containing an ether bond includes: a divalent group having an aromatic structure, two ether bonds, and two phthalic anhydride residues, and the two end groups of the divalent group having an aromatic structure are respectively connected to the phenyl group of a phthalic anhydride residue through an ether bond.

[0128] That is to say, the chemical structural formula of the polymer provided by the embodiments of the present disclosure is as shown below, and this polymer can be simply referred to as a polyetherimide polymer:

[0129] 0000338Among them, is a divalent group having an aromatic structure;

[0131] R 1 is a diamine residue having an alicyclic structure;

[0132] R 2 is a diamine residue having a polar functional group.

[0133] Among them, for this group is the above-mentioned aromatic dianhydride residue containing an ether bond.

[0134] In some possible implementation manners, the number m of the first repeating units and the number n of the second repeating units are both integers, 0 < m ≤ 500, 0 ≤ n ≤ 100, and n / m ≤ 1 / 4. Among them, limiting the numerical ranges of m and n as above can make the molecular weight of the polymer within the expected range to obtain a suitable viscosity; making n / m ≤ 1 / 4 can increase the amount of diamine residues having an alicyclic structure, thereby reducing the side reaction with lithium ions.

[0135] In some possible embodiments, a divalent group having an aromatic structure The invention comprises: a first phenyl group and an optional third repeating unit, wherein the third repeating unit comprises: a linking group and a second phenyl group; the first phenyl group is connected to one end group of the linking group in the third repeating unit, and the second phenyl group is connected to the other end group of the linking group; the first phenyl group and the second phenyl group are substituted or unsubstituted; the linking group is a single bond, -O-, -S-, -S(O)-, -SO2-, -C(O)- or C 1-18 Organic bridging group.

[0136] Exemplarily, the first phenyl group has a first substituent, and the first substituent is a halogen atom or a monovalent C 1-10 Alkyl group; the second phenyl group has a second substituent, the second substituent is a halogen atom or a monovalent C 1-10 an alkyl group; the number of the first substituent and the number of the second substituent are both 1-4. The halogen atom may be a chlorine atom, a bromine atom, a fluorine atom, or the like. Exemplarily, the number of the third repeating unit is 0-4, for example, 0, 1, 2, 3, or 4.

[0137] Based on the above, it can be seen that the divalent group with an aromatic structure The chemical structure is shown below:

[0138]

[0139] Among them, R a and R b Each independently is a halogen atom or a monovalent C 1-10 Alkyl group, wherein the monovalent C 1-10 The alkyl group refers to a saturated aliphatic group containing 1 to 10 carbon atoms, including straight-chain alkyl and branched-chain alkyl, for example, methyl, ethyl, propyl, butyl, etc. a and R b It can be the same or different.

[0140] X a is a single bond, -O-, -S-, -S(O)-, -SO2-, -C(O)- or C 1-18 Organic bridging group, wherein the C 1-18 The organic bridging group refers to a bridging group containing 1 to 18 carbon atoms. 1-18 The organic bridging group may be cyclic or acyclic, or the C 1-18 The organic bridging group may be aromatic or non-aromatic. 1-18 The organic bridging group may further contain heteroatoms, for example, the heteroatoms include but are not limited to halogen atoms, oxygen atoms, nitrogen atoms, sulfur atoms or fluorine atoms.

[0141] p, q and c are each independently an integer of 0-4, wherein p, q and c may be the same, different, or partially the same, and p, q and c are not 0 at the same time.

[0142] In some possible implementations, for the polymer provided in the embodiments of the present disclosure, the diamine residue having an aliphatic ring structure comes from at least one of the following aliphatic ring-containing diamine monomer compounds, that is, after at least one of the following aliphatic ring-containing diamine monomer compounds is used to participate in the polymerization reaction, the group of the aliphatic ring-containing diamine monomer compound remaining in the polymer is a diamine residue having an aliphatic ring structure.

[0143] The aliphatic ring-containing diamine monomer compound includes but is not limited to the following: 1,2-cyclohexanediamine, 1,3-cyclohexanediamine, 4-methyl-1,3-cyclohexanediamine, 1,4-cyclohexanediamine, trans-1,4-cyclohexanediamine, cis-1,4-cyclohexanediamine, 1,4-diaminomethylcyclohexane, 1,3-diaminomethylcyclohexane, bis(aminomethyl)norbornane, isophoronediamine, adamantane-1,3-diamine, 2,2'-bis(trifluoromethyl)-4,4'-diamino-chain cyclohexane, 4,4'-methylenebis(cyclohexylamine), 4,4'-methylenebis(2-methylcyclohexylamine), 2,2'-bis(4-aminocyclohexyl)hexafluoropropane, and 1,1'-diadamantane-3,3'-diamine.

[0144] The diamine residue with an aliphatic ring structure provided by the above-mentioned aliphatic ring-containing diamine monomer can effectively inhibit the formation of charge transfer complexes within or between polymer molecules, reduce the side reaction between polyetherimide and lithium ions, and thus reduce the consumption of active lithium, which is beneficial to improving the coulombic efficiency and first efficiency of lithium-ion batteries.

[0145] In some possible implementations, the diamine residue having a polar functional group is selected from at least one of a carboxyl group, a hydroxyl group, and a sulfonic acid group. These polar functional groups can increase the adhesion between the polymer and the silicon-based negative electrode material, the carbon material, and the current collector.

[0146] In some possible implementations, for the polymer provided in the embodiments of the present disclosure, the diamine residue having a polar functional group comes from at least one of the following diamine monomer compounds containing polar groups. That is, after at least one of the following diamine monomer compounds containing polar groups is used to participate in the polymerization reaction, the group of the diamine monomer compound containing polar groups remaining in the polymer is a diamine residue having a polar functional group.

[0147] The diamine monomer compound containing a polar group includes but is not limited to the following: 3,5-diaminocyclohexanecarboxylic acid, 3,5-diaminobenzoic acid, 4,4'-diaminobiphenyl-2,2'-dicarboxylic acid, 5,5'-methylenebis(2-aminobenzoic acid), 3,3'-dihydroxybenzidine, 2,2'-bis(3-amino-4-hydroxyphenyl)propane, 2,2'-bis(3-amino-4-hydroxyphenyl)hexafluoropropane, ... (3-Amino-4-hydroxyphenyl) sulfone, 4,6-diaminoresorcinol dihydrochloride, 2,5-diamino-1,4-benzenedithiol dihydrochloride, 2,6-dihydroxy-3,7-diaminotrisole, 2,2'-bis[3-(4-aminobenzamido)-4-hydroxyphenyl]hexafluoropropane, 4,4'-diamino-2,2'-biphenyldisulfonic acid, 4,4'-diaminostilbene-2,2'-disulfonic acid.

[0148] The diamine residue with polar functional groups provided by the above-mentioned diamine monomer containing polar groups can effectively increase the adhesion between the polymer and the silicon-based negative electrode material, carbon material and current collector, making the negative electrode sheet less likely to crack and pulverize during the charge and discharge process, ensuring that the lithium-ion battery maintains sufficient capacity and has stronger cycle stability.

[0149] In summary, some exemplary polymers are given below, and their chemical structural formulas are shown below:

[0150]

[0151] According to another aspect of the present disclosure, a method for preparing a polymer is provided. The polymer is as described above, and the method for preparing the polymer comprises:

[0152] Under the action of an inert atmosphere and a catalyst, a dianhydride monomer, an aliphatic ring-containing diamine monomer, and an optional polar group-containing diamine monomer are polymerized in a first solvent to obtain a polymer.

[0153] In some examples, the chemical structure of the polymers mentioned above is as follows:

[0154]

[0155] in, It is a divalent group with an aromatic structure;

[0156] R 1 It is a diamine residue with an alicyclic structure;

[0157] R 2 is a diamine residue having a polar functional group;

[0158] Both m and n are integers, where 0 < m ≤ 500, 0 ≤ n ≤ 100, and n / m ≤ 1 / 4.

[0159] Among them, the dianhydride monomer includes: a divalent group with an aromatic structure, two ether bonds, and two phthalic anhydride groups; two end groups of the divalent group with an aromatic structure are respectively connected to the phenyl group of a phthalic anhydride group through an ether bond.

[0160] Based on the above, the chemical structural formula of the dianhydride monomer is as follows:

[0161]

[0162] R 1 is a diamine residue with an alicyclic structure, that is, the group remaining in the polymer after the polymerization reaction of the alicyclic diamine monomer.

[0163] R 2 is a diamine residue with a polar functional group, that is, the group remaining in the polymer after the polymerization reaction of the diamine monomer containing a polar group.

[0164] According to the above chemical structural formula of the polymer, if the usage amount of the dianhydride monomer is x mol, the usage amount of the alicyclic diamine monomer is y mol, and the usage amount of the diamine monomer containing a polar group is z mol, then x = y + z.

[0165] A protective atmosphere for the polymerization reaction is provided through an inert atmosphere to prevent unwanted oxidation of each component during the polymerization reaction. This inert atmosphere can be a nitrogen atmosphere, an argon atmosphere, etc.

[0166] The preparation method of the polymer provided by the embodiments of the present disclosure enables the dianhydride monomer, the alicyclic diamine monomer, and optionally the diamine monomer containing a polar group to carry out a polymerization reaction in a first solvent, thereby enabling the preparation of a polymer with the above chemical structural formula.

[0167] In some possible implementation manners, the divalent group with an aromatic structure includes: a first phenyl group and an optional third repeating unit. The third repeating unit includes: a linking group and a second phenyl group; the first phenyl group is connected to the first end group of the linking group in the third repeating unit, and the second phenyl group is connected to the second end group of the linking group; the first phenyl group and the second phenyl group are substituted or unsubstituted; the linking group is a single bond, -O-, -S-, -S(O)-, -SO2-, -C(O)- or C 1-18 organic bridging group; the number of the third repeating unit is 0 - 4.

[0168] Exemplarily, the first phenyl group has a first substituent, and the first substituent is a halogen atom or a monovalent C 1-10Alkyl group; the second phenyl group has a second substituent, the second substituent is a halogen atom or a monovalent C 1-10 an alkyl group; the number of the first substituent and the number of the second substituent are both 1-4.

[0169] Based on the above, it can be seen that the divalent group with an aromatic structure The chemical structure is shown below:

[0170]

[0171] Among them, R a and R b Each independently is a halogen atom or a monovalent C 1-10 Alkyl group, wherein the monovalent C 1-10 The alkyl group refers to a saturated aliphatic group containing 1 to 10 carbon atoms, including straight-chain alkyl and branched-chain alkyl, for example, methyl, ethyl, propyl, butyl, etc. a and R b It can be the same or different.

[0172] X a is a single bond, -O-, -S-, -S(O)-, -SO2-, -C(O)- or C 1-18 Organic bridging group, wherein the C 1-18 The organic bridging group refers to a bridging group containing 1 to 18 carbon atoms. 1-18 The organic bridging group may be cyclic or acyclic, or the C 1-18 The organic bridging group may be aromatic or non-aromatic. 1-18 The organic bridging group may further contain heteroatoms, for example, the heteroatoms include but are not limited to halogen atoms, oxygen atoms, nitrogen atoms, sulfur atoms or fluorine atoms.

[0173] p, q and c are each independently an integer of 0-4, wherein p, q and c may be the same, different, or partially the same, and p, q and c are not 0 at the same time.

[0174] In some possible implementations, the aliphatic ring-containing diamine monomer is selected from at least one of the following compounds: 1,2-cyclohexanediamine, 1,3-cyclohexanediamine, 4-methyl-1,3-cyclohexanediamine, 1,4-cyclohexanediamine, trans-1,4-cyclohexanediamine, cis-1,4-cyclohexanediamine, 1,4-diaminomethylcyclohexane, 1,3-diaminomethylcyclohexane, bis(aminomethyl)norbornane, isophoronediamine, adamantane-1,3-diamine, 2,2'-bis(trifluoromethyl)-4,4'-diamino-chain cyclohexane, 4,4'-methylenebis(cyclohexylamine), 4,4'-methylenebis(2-methylcyclohexylamine), 2,2'-bis(4-aminocyclohexyl)hexafluoropropane, and 1,1'-diadamantane-3,3'-diamine.

[0175] The diamine residue with an aliphatic ring structure provided by the above-mentioned aliphatic ring-containing diamine monomer can effectively inhibit the formation of charge transfer complexes within or between polymer molecules, reduce the side reaction between polyetherimide and lithium ions, and thus reduce the consumption of active lithium, which is beneficial to improving the coulombic efficiency and first efficiency of lithium-ion batteries.

[0176] In some possible implementations, the polar group-containing diamine monomer is selected from at least one of the following compounds: 3,5-diaminocyclohexanecarboxylic acid, 3,5-diaminobenzoic acid, 4,4'-diaminobiphenyl-2,2'-dicarboxylic acid, 5,5'-methylenebis(2-aminobenzoic acid), 3,3'-dihydroxybenzidine, 2,2'-bis(3-amino-4-hydroxyphenyl)propane, 2,2'-bis(3-amino-4-hydroxyphenyl)hexafluoropropane, bis(3-amino-4-hydroxyphenyl)sulfone, 4,6-diaminoresorcinol dihydrochloride, 2,5-diamino-1,4-benzenedithiol dihydrochloride, 2,6-dihydroxy-3,7-diaminotrisole, and 2,2'-bis[3-(4-aminobenzamido)-4-hydroxyphenyl]hexafluoropropane.

[0177] The diamine residue with polar functional groups provided by the above-mentioned diamine monomer containing polar groups can effectively increase the adhesion between the polymer and the silicon-based negative electrode material, carbon material and current collector, making the negative electrode sheet less likely to crack and pulverize during the charge and discharge process, ensuring that the lithium-ion battery maintains sufficient capacity and has stronger cycle stability.

[0178] The polymerization reaction is carried out in a liquid environment provided by a first solvent. In some possible implementations, the first solvent includes at least one of a phenolic solvent, a polyhalogenated benzene solvent, N,N-dimethylacetamide, N-methyl-2-pyrrolidone, nitrobenzene, and benzonitrile. Examples of the phenolic solvent include m-cresol and p-chlorophenol, and examples of the polyhalogenated benzene solvent include o-dichlorobenzene.

[0179] The first solvent can not only dissolve the dianhydride monomer, the aliphatic ring-containing diamine monomer, and the polar group-containing diamine monomer, but also has a smaller chain transfer constant, which is beneficial for the polymerization reaction to proceed fully and thoroughly, and the polymerization reaction is faster.

[0180] In some possible implementations, the catalyst suitable for the polymerization reaction includes at least one of isoquinoline, triethylamine, benzoic acid, and p-hydroxybenzoic acid. Under the catalytic action of the catalyst, the polymerization reaction can be initiated quickly and effectively.

[0181] Isoquinoline and triethylamine are alkaline catalysts, while benzoic acid and p-hydroxybenzoic acid are acidic catalysts. A suitable catalyst can be adaptively selected according to the specific reaction system as long as the desired degree of polymerization is obtained.

[0182] In some examples, only one catalyst may be used, while in other examples, multiple catalysts may be used. For example, an acidic catalyst such as benzoic acid may be added first. If the polymerization degree improvement effect is poor, a basic catalyst such as isoquinoline may be further added.

[0183] In some examples, a dianhydride monomer, an aliphatic ring-containing diamine monomer, and an optional polar group-containing diamine monomer are polymerized in a first solvent under an inert atmosphere and a catalyst, comprising the following steps:

[0184] Step a: uniformly mix the dianhydride monomer, the aliphatic ring-containing diamine monomer, and the optional polar group-containing diamine monomer with a first solvent to obtain a first mixed solution.

[0185] Step b: uniformly mixing the first mixed liquid and the catalyst at a first set temperature to obtain a second mixed liquid.

[0186] Step c: subjecting the second mixed solution to a polymerization reaction at a second set temperature to obtain a reaction product solution containing a polymer.

[0187] Step d: separating and treating the reaction product solution containing the polymer to obtain the polymer.

[0188] In step b, the first mixed liquid and the catalyst are uniformly mixed at a first set temperature to obtain a second mixed liquid. Exemplarily, the first set temperature is 75° C. to 90° C., such as 75° C., 77° C., 79° C., 80° C., 81° C., 82° C., 83° C., 84° C., 85° C., 88° C., etc. Within this temperature range, the dianhydride monomer, the aliphatic ring-containing diamine monomer, the polar group-containing diamine monomer, and the catalyst can be fully dissolved in the first solvent to form a second mixed liquid with a uniform texture.

[0189] In step c, the second mixed liquid is subjected to a polymerization reaction at a second set temperature to obtain a reaction product solution containing a polymer. Exemplarily, the second set temperature is 160° C. to 200° C., for example, 160° C., 165° C., 170° C., 175° C., 180° C., 185° C., 190° C., 195° C., 200° C., etc. Within this temperature range, the polymerization reaction can proceed sufficiently, thoroughly, rapidly, and controllably, thereby facilitating the production of a polymer having a desired molecular weight.

[0190] In some possible implementations, a first mixed solution is formed from a dianhydride monomer, an aliphatic ring-containing diamine monomer, a polar group-containing diamine monomer, and a first solvent. The solid content of the first mixed solution is 20 wt%-40 wt%, for example, 20 wt%, 22 wt%, 25 wt%, 27 wt%, 30 wt%, 32 wt%, 35 wt%, 38 wt%, 40 wt%, etc. The solid content of the first mixed solution within the above range allows the first mixed solution to have an appropriate viscosity, sufficiently disperse the above components, and prevent sedimentation after being left for a certain period of time.

[0191] In step d, the polymer-containing reaction product solution is subjected to a separation treatment, comprising:

[0192] Step d1: uniformly mixing the polymer-containing reaction product solution with the second solvent to obtain a third mixed solution having a solid content of 3 wt% to 7 wt%. For example, the solid content of the third mixed solution includes, but is not limited to, 3 wt%, 4 wt%, 5 wt%, 6 wt%, 7 wt%, etc.

[0193] Step d2: using the precipitate to precipitate the third mixed solution to separate and obtain a first solid reaction product.

[0194] Step d3: extracting the first solid reaction product with an extracting solution to obtain a second solid reaction product.

[0195] Step d4: drying the second solid reaction product to obtain polyetherimide.

[0196] In step d1, the second solvent is selected to be a good solvent for the above-mentioned monomers to elute the unreacted monomers from the polyetherimide, so as to obtain high-purity polyetherimide.

[0197] In some examples, the second solvent includes at least one of a phenolic solvent, a polyhalogenated benzene solvent, N,N-dimethylacetamide, N-methyl-2-pyrrolidone, nitrobenzene, and benzonitrile. The phenolic solvent may be, for example, m-cresol or p-chlorophenol, and the polyhalogenated benzene solvent may be, for example, o-dichlorobenzene.

[0198] In some examples, a second solvent is added to the reactor containing the reaction product solution, the amount of the second solvent being such that the solid content of the third mixed solution is 3 wt % to 7 wt %, and the temperature of the third mixed solution is naturally cooled to room temperature.

[0199] For step d2, the applicable precipitate includes but is not limited to at least one of methanol, ethanol, and deionized water to remove unreacted monomers and incompletely polymerized oligomers with smaller molecular weights.

[0200] In some examples, the third mixed liquid is added to a stirrer with a precipitate and maintained in a magnetic stirring state until a filamentous first solid reaction product (a white fibrous solid) is precipitated, and then filtered to separate the first solid reaction product.

[0201] For step d3, the applicable extraction solution includes but is not limited to at least one of methanol, ethanol, and deionized water to remove the solvent in the system.

[0202] In some examples, the first solid reaction product and the extract are placed in a Soxhlet extractor, heated and refluxed for 12 hours to 48 hours to remove excess first solvent and second solvent, and reflux out the second solid reaction product.

[0203] In step d4, in some examples, after the reflow is completed, a drying treatment, such as an oven drying treatment, is performed at a temperature of 100° C. to 140° C. to obtain a polymer.

[0204] In some possible implementations, the specific steps of the polymerization reaction involved in the embodiments of the present disclosure are as follows:

[0205] Under nitrogen, a dianhydride monomer (x mmol), an aliphatic ring-containing diamine monomer (y mmol), and a polar functional group-containing diamine monomer (z mmol) are added to a polymerization bottle (x=y+z). The raw materials on the wall of the polymerization bottle are rinsed off with a first solvent, and the solid content of the system is controlled to be 20wt%-40wt%. After stirring at room temperature for 20-100 minutes, a catalyst is added, and the temperature is raised to 75°C-90°C with stirring until the reactants are completely dissolved. The temperature is then raised to 160°C-200°C and the reaction is carried out at this temperature for 6-12 hours to produce a viscous reaction product solution containing a polymer.

[0206] Subsequently, the second solvent is continuously added to the polymerization bottle to dilute the solid content of the product system to 3 wt % to 7 wt %, and heating is stopped, and the temperature is naturally lowered to room temperature.

[0207] The product solution is added to a stirrer with a precipitate, and magnetic stirring is maintained until a first solid reaction product (a white fibrous solid) is precipitated, which is then filtered to separate the first solid reaction product. The first solid reaction product and the extract are both placed in a Soxhlet extractor, heated and refluxed for 12-48 hours to remove excess first and second solvents, and a second solid reaction product is refluxed. After the reflux is completed, the mixture is dried at a temperature of 100-140°C to obtain a polymer.

[0208] For example, the chemical equation for the polymerization reaction involving 4,4'-bisphenol A diether dianhydride (BPADA), 1,4-cyclohexanediamine (1,4-CHDA), and 2,2'-diaminobiphenyl (2,2'-DCB) is shown below:

[0209]

[0210] The specific steps of the polymerization reaction can be as follows:

[0211] Under nitrogen, 4,4'-bisphenol A diether dianhydride (BPADA) (10.4023 g, 20 mmol), 4,4'-diaminobiphenyl-2,2'-dicarboxylic acid (2,2'-DCB) (1.0883 g, 4 mmol), and 1,4-cyclohexanediamine (1,4-CHDA) (1.8258 g, 16 mmol) were added to a polymerization flask. The chemicals on the flask walls were rinsed with m-cresol to control the solid content of the system to 30 wt%. After stirring at room temperature for 30 minutes, the reaction system was heated to 80°C and stirred until the reaction system was completely dissolved. The reaction system was then heated to 180°C and the reaction continued for 6-12 hours, until the polymerization reaction was fully and thoroughly completed, producing a viscous reaction product solution containing the polymer.

[0212] Subsequently, m-cresol was added to the polymerization bottle to dilute the solid content of the product system to 5 wt %, and heating was stopped, and the temperature was naturally cooled to room temperature.

[0213] The product solution is added to a stirrer containing methanol and magnetically stirred until a filamentous white fibrous solid precipitates, which is then filtered to separate the white fibrous solid. The white fibrous solid and methanol are placed in a Soxhlet extractor and heated and refluxed for 12 to 48 hours to remove excess m-cresol and reflux the solid reaction product. After reflux, the product is dried at 120°C to obtain a polymer having the above chemical formula.

[0214] According to another aspect of the embodiments of the present disclosure, the embodiments of the present disclosure further provide a negative electrode material, which includes a binder, an active material, and a conductive agent; wherein, the binder includes any one of the polymers shown above in the embodiments of the present disclosure; the active material includes a silicon-based negative electrode material.

[0215] For the binder provided in the embodiments of the present disclosure, the polymers involved can be the same one or different ones, that is, multiple polymers can have multiple different chemical structures. That is to say, the same chemical structure of polymer can be used in the negative electrode material, or a combination of multiple polymers with multiple different chemical structures can be used.

[0216] In some possible examples, the binder of the negative electrode material can further include other polyimide compounds. For example, the polyimide compounds include, but are not limited to: fully aromatic polyimides, polyetherimides, polyamide-imides, etc., to further improve the mechanical strength of the binder.

[0217] The active material can use the silicon-based negative electrode material alone. Further, the active material can also include a carbon-based negative electrode material (that is, it includes both a silicon-based negative electrode material and a carbon-based negative electrode material). The weight percentage of the silicon-based negative electrode material in the active material is 1 wt% - 99.5 wt%. For example, the weight percentage of the silicon-based negative electrode material in the active material is 50 wt% - 99.5 wt%. Further, for example, this includes, but is not limited to: 50 wt%, 55 wt%, 60 wt%, 65 wt%, 70 wt%, 75 wt%, 80 wt%, 85 wt%, 90 wt%, 95 wt%, etc. By using the silicon-based negative electrode material in combination with the carbon-based composite material, it is beneficial to further improve the capacity of the negative electrode material.

[0218] In the embodiments of the present disclosure, the silicon-based negative electrode material includes at least one of silicon, silicon oxide material, and silicon carbide material. Among them, silicon includes, but is not limited to: polysilicon nanoparticles, polysilicon nanowires, silicon-based alloy powders, amorphous silicon particles, graphene-wrapped amorphous silicon particles, etc.; the chemical formula of the silicon oxide is SiO x (0 < x ≤ 2), for example, silicon dioxide, silicon monoxide, etc.

[0219] The carbon-based negative electrode material includes at least one of graphite, hard carbon, and soft carbon. Among them, graphite includes, but is not limited to: natural graphite, artificial graphite, surface-modified natural graphite, etc.

[0220] In some examples, the weight percentage of the polymer in the negative electrode material is 1 wt%-20 wt%; the weight percentage of the conductive agent in the negative electrode material is 1 wt%-20 wt%; and the active material is the balance. The active material being the balance means that the amount of active material is such that the total weight percentage of the polymer, active material, and conductive agent is 100%.

[0221] The weight percentage of the polymer in the negative electrode material is 1 wt%-20 wt%, for example, 3 wt%-15 wt%, for example, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, etc. Within the above weight percentage range, the polymer can ensure adhesion and inhibit expansion of the silicon active material, while reducing the internal resistance of the negative electrode sheet and increasing the proportion of the silicon-based negative electrode material.

[0222] The weight percentage of the conductive agent in the negative electrode material is 1wt%-20wt%, for example, 3wt%-15wt%, and further examples include 5%, 6%, 7%, 8%, 9%, 10%, etc. Suitable conductive agents are sufficient as long as they do not provide additional capacity, do not cause additional chemical reactions, and have electronic conductivity. In some examples, the conductive agent includes but is not limited to at least one of conductive graphite, conductive carbon black, acetylene black, carbon nanotubes, and graphene. Use of such conductive agents can reduce the impedance of the negative electrode sheet and improve rate performance.

[0223] In some examples, in the negative electrode material, the weight percentages of the active material, the conductive agent, and the binder are 86 wt %, 6 wt %, and 8 wt %, respectively.

[0224] In the negative electrode materials provided by the embodiments of the present disclosure, the polymer acts as a binder, exhibiting high mechanical strength and adhesion. This allows the silicon-based negative electrode material and the conductive agent in the active material to bond together, achieving high bonding strength. Furthermore, the polymer also helps improve the bonding strength between the silicon-based negative electrode material, the conductive agent, and the current collector, making the negative electrode less susceptible to cracking and pulverization during charge and discharge. This helps lithium-ion batteries maintain sufficient capacity, improve their energy density, and provide greater cycling stability.

[0225] In addition, due to the high elastic modulus, good toughness, and high mechanical strength of the polymer, when it is used as a binder to prepare a negative electrode sheet, even if the negative electrode sheet contains a higher silicon content, it can suppress the volume expansion of the silicon-based negative electrode material, prevent the peeling and collapse at the interface between the conductive agent and the current collector due to the volume change of the silicon-based negative electrode material during the charge and discharge process, and thus maintain the structural stability of the negative electrode sheet, which is conducive to the lithium-ion battery maintaining sufficient capacity and having stronger cycle stability. The polymer provided by the embodiment of the present disclosure, based on its diamine residue with an alicyclic structure, reduces the use of aromatic groups, can effectively inhibit the formation of charge transfer complexes within or between polymer molecules, and reduce the side reaction of polyetherimide with lithium ions, which is conducive to further improving the coulombic efficiency and first effect of the lithium-ion battery.

[0226] According to another aspect of the embodiments of the present disclosure, the embodiments of the present disclosure also provide a negative electrode plate, which includes: an active material layer and a current collector, the active material layer is located on at least one surface of the current collector, for example, on two opposite surfaces of the current collector, and the active material layer is prepared using the above-mentioned negative electrode material.

[0227] Exemplarily, the method for preparing the negative electrode sheet is as follows:

[0228] The polymer is dissolved in a polar solvent to obtain a glue solution; the glue solution is mixed with the active material and the conductive agent and stirred evenly to obtain a negative electrode slurry; the negative electrode slurry is coated on two opposite surfaces of the current collector, and then dried and rolled to obtain a negative electrode sheet.

[0229] In order to improve the quality of the negative electrode sheet, the negative electrode slurry can be degassed and screened, and then coated on two opposite surfaces of the current collector.

[0230] It can be seen that when the polymer provided in the embodiment of the present disclosure is used as a binder to prepare the negative electrode plate, no additional high-temperature or chemical treatment steps are required, and only simple coating and drying treatments are required. This not only significantly reduces the processing difficulty of the negative electrode plate, but also effectively avoids the problem of degradation of the negative electrode plate performance due to oxidation of the silicon active material or current collector caused by high-temperature post-treatment.

[0231] The current collector includes but is not limited to at least one of copper foil, copper mesh, carbon-coated copper foil, stainless steel foil, stainless steel mesh, carbon-coated stainless steel foil, and nickel foil.

[0232] In some examples, the current collector can be obtained through a calendering process, for example, using rolled copper foil or stainless steel foil with higher tensile strength. This is because when a silicon-based negative electrode material with a large volume change is combined with a polymer with high adhesion and high mechanical strength, if it is coated on an electrolytic copper foil with lower tensile strength, it can easily cause the negative electrode sheet to stretch in the length and width direction, and even cause the negative electrode sheet to break or shatter during the charge and discharge cycle of the lithium-ion battery. Using rolled copper foil and stainless steel foil with higher tensile strength can effectively avoid the above technical problems and ensure the structural stability of the negative electrode sheet during the charge and discharge cycle.

[0233] Wherein, a polar solvent is used to dissolve the polymer. In some examples, the polar solvent includes but is not limited to at least one of N-methylpyrrolidone, dimethylacetamide, N,N-dimethylformamide, dimethyl sulfoxide, and cyclohexanone.

[0234] The weight percentage of the polymer in the glue solution is 1 wt%-50 wt%, for example, 5 wt%-2 wt%.

[0235] According to another aspect of the embodiments of the present disclosure, the embodiments of the present disclosure further provide a lithium-ion battery, which includes the above-mentioned negative electrode plate provided by the embodiments of the present disclosure.

[0236] Based on the use of the negative electrode plate provided by the embodiments of the present disclosure, the lithium-ion battery has at least the following advantages:

[0237] The negative electrode sheet is not prone to cracking and pulverization during the charge and discharge process. Even if the negative electrode sheet contains a higher silicon content, it can suppress the volume expansion of the silicon-based negative electrode material, prevent the peeling and collapse at the interface between the conductive agent and the current collector due to the volume change of the silicon-based negative electrode material during the charge and discharge process, and thus maintain the structural stability of the negative electrode sheet. This helps the lithium-ion battery maintain sufficient capacity and has stronger cycle stability. Based on the polymer used, the probability of lithium ions in the lithium-ion battery undergoing side reactions is significantly reduced, ensuring that there is always sufficient active lithium, which is conducive to improving the coulombic efficiency and first efficiency of the lithium-ion battery.

[0238] The lithium ion battery provided by the embodiment of the present disclosure is as follows Figure 1 As shown, the lithium-ion battery includes not only the negative electrode sheet 100 , but also a positive electrode sheet 200 , an electrolyte 300 , a separator 400 , and an encapsulation layer 500 .

[0239] The electrolyte 300 is filled in the space between the negative electrode sheet 100 and the positive electrode sheet 200. The separator 400 is located in the electrolyte 300 and is used to separate the negative electrode sheet 100 from the positive electrode sheet 200. The encapsulation layer 500 is used to encapsulate the negative electrode sheet 100, the positive electrode sheet 200, the electrolyte 300, and the separator 400.

[0240] Lithium-ion batteries store and release energy by intercalating and deintercalating lithium ions between the negative electrode sheet 100 and the positive electrode sheet 200. The electrolyte 300 is a carrier for the transmission of lithium ions between the negative electrode sheet 100 and the positive electrode sheet 200. The diaphragm 400 is ion conductive but electronically insulating. The diaphragm 400 is used to ensure the migration of lithium ions while separating the negative electrode sheet 100 and the positive electrode sheet 200 to prevent short circuits.

[0241] The positive electrode plate 200 includes a positive electrode active material, a conductive agent, a current collector and a positive electrode binder, wherein the positive electrode active material includes but is not limited to: at least one of lithium-containing layered metal oxides, lithium-containing spinel structure metal oxides, lithium metal phosphates, lithium metal fluoride sulfates and lithium metal vanadates.

[0242] For example, lithium-containing layered metal oxides include but are not limited to at least one of lithium cobalt oxide (LiCoO2), nickel-cobalt-manganese ternary material (NCM), and nickel-cobalt-aluminum ternary material (NCA); lithium-containing spinel structure metal oxides include but are not limited to lithium manganese oxide (LiMn2O4), etc.; lithium metal phosphates include but are not limited to lithium iron phosphate (LiFePO4), etc.; lithium metal fluoride sulfates include but are not limited to lithium cobalt fluoride sulfate (LiCoFSO4), etc.; lithium metal vanadates include but are not limited to lithium nickel vanadate (LiNiVO4), etc.

[0243] The conductive agent used in the positive electrode plate includes, but is not limited to, at least one of conductive graphite, conductive carbon black, acetylene black, carbon nanotubes, and graphene. For the positive electrode plate, the weight of the conductive agent is 1% to 8% by weight of the total mass of the positive electrode active material, conductive agent, and positive electrode binder, for example, 2% to 5% by weight.

[0244] The present disclosure will be further described below through more specific examples. Although some specific embodiments are described below, it should be understood that the present disclosure can be implemented in various forms and should not be limited by the examples set forth herein. Where specific techniques or conditions are not specified in the examples, the techniques or conditions described in the literature in the art or in accordance with the product instructions are used. Where the manufacturer of the reagents or instruments is not specified, they may be conventional products that can be obtained commercially.

[0245] The N / P involved in the following embodiments, that is, negative / positive, refers to (negative electrode active material gram capacity × negative electrode areal density × negative electrode active material content ratio) ÷ (positive electrode active material gram capacity × positive electrode areal density × positive electrode active material content ratio).

[0246] Example 1

[0247] (1.1) Synthesis of 1# polyetherimide adhesive

[0248] Under nitrogen, 4,4'-bisphenol A diether dianhydride (BPADA) (10.4023 g, 20 mmol) and 1,3-cyclohexanediamine (1,3-CHDA) (2.2823 g, 20 mmol) were added to a polymerization flask. The chemicals on the flask walls were rinsed with m-cresol to control the solid content of the reaction system to 30 wt%. After stirring at room temperature for 30 minutes, the reaction system was heated to 80°C and stirred until the reaction system was completely dissolved. The reaction system was heated to 180°C and the reaction continued for approximately 10-12 hours, until all monomers reacted completely, to produce a viscous reaction product solution containing the polymer.

[0249] Subsequently, m-cresol was added to the polymerization bottle to dilute the solid content of the product system to 5wt%, and heating was stopped and the temperature was naturally reduced to room temperature. The product solution was added to a stirrer with methanol and maintained in a magnetic stirring state until a filamentous white fiber solid was precipitated, and then filtered to separate the white fiber solid. The white fiber solid and methanol were placed in a Soxhlet extractor, heated and refluxed for 30 hours to remove excess m-cresol, and the solid reaction product was refluxed. After the reflux was completed, the product was dried at a temperature of 120°C to obtain the above-mentioned 1# polymer as a binder.

[0250] The chemical structure of the polymer #1 is as follows:

[0251]

[0252] (1.2) Preparation of 1# negative electrode sheet

[0253] According to the ratio of silicon dioxide active material: conductive carbon black: 1# polyetherimide binder = 86wt%: 6wt%: 8wt%, 1# polyimide binder is dissolved in N-methylpyrrolidone to prepare a glue with a weight fraction of 20wt% for use. Conductive carbon black and silicon dioxide active material are added to the glue step by step, and stirred at a high speed of 2000rpm for 2 hours to obtain a uniformly dispersed negative electrode slurry. After degassing and screening the negative electrode slurry, the negative electrode slurry is coated on both sides of the rolled copper foil, vacuum baked at 110℃ overnight, and rolled by a roller press to obtain 1# negative electrode sheet. Among them, the density of 1# negative electrode sheet is 1.5g / cc, and the surface capacity is 4mAh / cm 2 .

[0254] (1.3) Preparation of No. 1 lithium-ion battery

[0255] The No. 1 negative electrode sheet was die-cut and stacked with a lithium cobalt oxide positive electrode sheet (LiCoO2: conductive carbon black: PVDF binder = 95wt%: 2wt%: 3wt%; N / P = 1 / 1) with matching capacity to prepare a No. 1 soft-pack lithium-ion battery (capacity of 550mAh).

[0256] Example 2

[0257] The same binder synthesis method and negative electrode sheet preparation method as in Example 1 were used to prepare polymer 2# and negative electrode sheet 2#. The differences are:

[0258] The monomers involved in the preparation of polymer 2# are as follows: 20 mmol of 4,4'-bisphenol A diether dianhydride (BPADA), 16 mmol of 1,4-cyclohexanediamine (1,4-CHDA), and 4 mmol of 3,5-diaminobenzoic acid (DABA). The chemical structure of polymer 2# is as follows, where x:y = 4:1:

[0259]

[0260] The 2# negative electrode sheet was prepared using the 2# polymer. The density of the 2# negative electrode sheet was 1.5g / cc and the surface capacity was 4mAh / cm 2 .

[0261] A 2# lithium-ion battery was prepared using the 2# negative electrode sheet. The 2# negative electrode sheet was die-cut and stacked with a lithium cobalt oxide positive electrode sheet (LCO: conductive agent: PVDF binder = 95wt%: 2wt%: 3wt%; N / P = 1 / 1) with matching capacity to produce a 2# soft-pack lithium-ion battery (capacity 550mAh).

[0262] Comparative Example 1

[0263] The binder synthesis method and negative electrode sheet preparation method are basically the same as those in Example 1 to prepare 3# polymer and 3# negative electrode sheet. The difference is:

[0264] The monomers involved in the preparation of polymer #3 are as follows: 20 mmol of 4,4'-bisphenol A diether dianhydride (BPADA), 20 mmol of 1,3-phenylenediamine (MPD), and the chemical structure of polymer #3 is as follows:

[0265]

[0266] The 3# negative electrode sheet was used to prepare the 3# lithium-ion battery. The density of the 3# negative electrode sheet was 1.5g / cc and the surface capacity was 4mAh / cm 2 The 3# negative electrode sheet was die-cut and stacked with a lithium cobalt oxide positive electrode sheet (LCO: conductive agent: PVDF binder = 95wt%: 2wt%: 3wt%; N / P = 1 / 1) with matching capacity to produce a 3# soft-pack lithium-ion battery (capacity 550mAh).

[0267] Comparative Example 2

[0268] The conductive carbon black and silica active material were premixed at 50 rpm for 30 minutes in a ratio of 85 wt% to 6 wt% to 1% to 8 wt% for conductive carbon black and PAA binder (polyacrylic acid, Sichuan Yindile Technology Co., Ltd.). The CMC thickener was then added and kneaded and stirred for 1 hour. The PAA binder was then added and stirred at 2000 rpm for 2 hours to obtain a uniformly dispersed negative electrode slurry. After degassing and sieving, the negative electrode slurry was coated on both sides of copper foil, vacuum-baked at 110°C overnight, and rolled on a roller press to obtain a 4# negative electrode sheet. The 4# negative electrode sheet had a compaction density of 1.5 g / cc and a surface capacity of 4 mAh / cm2.

[0269] The 4# negative electrode sheet was die-cut and laminated with a lithium cobalt oxide positive electrode sheet (LCO: conductive agent: PVDF binder = 95wt%: 2wt%: 3wt%; N / P = 1 / 1) with matching capacity to produce a 4# soft-pack lithium-ion battery (capacity 550mAh).

[0270] Test Case

[0271] This test example performs performance tests on the negative electrode sheets and lithium-ion batteries provided in Examples 1-2 and Comparative Examples 1-2. Specific test items and results are shown in Table 1:

[0272] Table 1

[0273]

[0274] The electrode peel strength is tested using the following steps: Cut the negative electrode to be tested into a 2cm x 10cm strip test specimen. Adhere the negative electrode to the side to be tested with 3M double-sided tape and compact it with a roller to ensure complete adhesion between the 3M double-sided tape and the negative electrode. The other side of the double-sided tape is then attached to a stainless steel plate. Bend one end of the test specimen 180 degrees. Use a universal material testing machine to clamp the test specimen and the stainless steel plate, respectively, and stretch them. The force required to separate the negative electrode from the stainless steel plate during stretching is recorded in real time. The average of all the forces is the negative electrode peel strength.

[0275] The expansion rate of the negative electrode plate is measured by the following test steps: each lithium-ion battery is subjected to 10 charge and discharge tests, and then charged to different battery states of charge (SOC) (50%, 100%). The plate is then removed and disassembled, the surface of the negative electrode plate is cleaned with dimethyl carbonate solvent and dried, and the thickness of different areas of the negative electrode plate is measured using a screw micrometer. The average value is taken, and the difference between this average value and the initial thickness of the negative electrode plate is divided by the initial thickness of the negative electrode plate (the thickness of the remaining part after excluding the thickness of the current collector). The resulting value is the expansion rate of the negative electrode plate.

[0276] For the first coulombic efficiency, it is carried out through the following test steps:

[0277] The negative electrode sheet, separator, and lithium metal sheet were assembled into a button half-cell. The first charge and discharge capacity of the button half-cell was measured using a blue light tester CT2001A, and the first coulombic efficiency was calculated, where the first coulombic efficiency = first lithium removal capacity / first lithium insertion capacity × 100%.

[0278] The cycle retention rate is tested by the following steps:

[0279] The capacity retention rate of each of the above soft-pack lithium-ion batteries after 200 cycles at a charge and discharge rate of 0.5C / 0.7C, wherein 0.5C refers to a battery discharge C rate (charge and discharge rate) of 0.5C, and 0.7C refers to a battery discharge C rate (charge and discharge rate) of 0.7C.

[0280] As can be seen from Table 1, the thickness expansion of the negative electrode sheets using the polyetherimide binders of Example 1, Example 2, and Comparative Example 1 is significantly smaller than that of the negative electrode sheet using the PAA binder in Comparative Example 2, which indicates that the polyetherimide binder has a more obvious inhibitory effect on the expansion of the negative electrode sheet.

[0281] At the same time, the polyetherimide binders of Examples 1 and 2, due to their use of the chemical structures shown in the disclosed embodiments, improved the initial coulombic efficiency of the lithium-ion battery, which was significantly higher than the initial efficiency of the lithium-ion battery corresponding to the fully aromatic polyetherimide binder of Comparative Example 1, and was comparable to the initial coulombic efficiency of the lithium-ion battery using the PAA binder of Comparative Example 2. The inventors analyzed that this is because the polyetherimide binder provided by the disclosed embodiments introduces an alicyclic structure, which inhibits the formation of charge transfer complexes in the polyetherimide molecules, reduces the degree of side reactions between lithium and the polyetherimide binder, reduces the loss of active lithium, and improves the coulombic efficiency of the lithium-ion battery.

[0282] According to the results of the pole piece peeling force test, compared with Comparative Example 1, the introduction of polar functional groups in the polyetherimide structure can significantly improve the bonding performance of the binder under the same pole piece composition and preparation conditions, which is specifically manifested in the improvement of the pole piece peeling force. In addition, from the cycle retention rate data in Table 1, it can be seen that the use of the polyetherimide binder provided by the embodiment of the present disclosure can significantly improve the cycle performance of the lithium-ion battery. This is because the polyetherimide binder provided by the embodiment of the present disclosure not only has good mechanical properties and film-forming properties (forming a coating film on the surface of silicon particles), but also has a good bonding effect with silicon-based negative electrode materials, current collectors and conductive agents, and has a significant positive effect on reducing side reactions on the surface of silicon particles and inhibiting the pulverization of silicon particles. It increases the structural stability of the negative electrode during the cycle and can also ensure the electronic path of the pole piece in the later stage of the cycle, thereby significantly improving the cycle life of the lithium-ion battery.

[0283] Figure 2 and Figure 3 The optical microscope 3D photos of the negative electrode sheets of Example 2 and Comparative Example 2 after 50 cycles (the scale is 200 μm), respectively. Figure 2 It can be seen that the electrode structure of the negative electrode provided in Example 2 is still intact after 50 cycles. Figure 3 As can be seen, the negative electrode sheet using the PAA binder in Comparative Example 2 exhibited structural looseness and collapse. This indicates that the polyetherimide binder provided by the disclosed embodiments exhibits superior mechanical strength and adhesion compared to traditional PAA binders, effectively resisting the stress generated by the significant volume expansion of the silicon material during lithium insertion and extraction, maintaining the structural integrity of the negative electrode sheet and improving expansion and cycling performance.

[0284] The above description is only for the purpose of facilitating those skilled in the art to understand the technical solutions of the present disclosure and is not intended to limit the present disclosure. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present disclosure shall be included in the scope of protection of the present disclosure.

Claims

1. A negative electrode material, characterized in that The negative electrode material includes: a binder, an active material, and a conductive agent; the binder includes a polymer, and the active material includes a silicon-based negative electrode material; The chemical structural formula of the polymer is as follows: in, The divalent group has an aromatic structure, including a first phenyl group, a linking group and a second phenyl group, wherein the first phenyl group is connected to one end group of the linking group, and the second phenyl group is connected to the other end group of the linking group, the first phenyl group and the second phenyl group are substituted or unsubstituted, and the linking group is a single bond, -O-, -S-, -S(O)-, -SO2-, -C(O)- or C 1-18 organic bridging group; R 1 The diamine residue having an aliphatic cyclic structure is derived from at least one of the following aliphatic ring-containing diamine monomer compounds: 1,2-cyclohexanediamine, 1,3-cyclohexanediamine, 4-methyl-1,3-cyclohexanediamine, 1,4-cyclohexanediamine, 1,4-diaminomethylcyclohexane, 1,3-diaminomethylcyclohexane, bis(aminomethyl)norbornane, isophoronediamine, adamantane-1,3-diamine, 2,2'-bis(trifluoromethyl)-4,4'-diamino-chain hexane, 4,4'-methylenebis(cyclohexylamine), 4,4'-methylenebis(2-methylcyclohexylamine), 2,2'-bis(4-aminocyclohexyl)hexafluoropropane, and 1,1'-diadamantane-3,3'-diamine. R 2 is a diamine residue having a polar functional group; Both m and n are integers, 0 < m ≤ 500, 0 ≤ n ≤ 100, and n / m ≤ 1 / 4.

2. The negative electrode material according to claim 1, characterized in that The first phenyl group has a first substituent, and the first substituent is a halogen atom or a monovalent C 1-10 alkyl groups; The second phenyl group has a second substituent, and the second substituent is a halogen atom or a monovalent C 1-10 alkyl groups; The number of both the first substituent and the second substituent is 1-4.

3. The negative electrode material according to claim 1, characterized in that The linking group and the second phenyl group form a repeating unit, and the number of the repeating units is 1-4.

4. The negative electrode material according to claim 1, characterized in that The polar functional group is selected from at least one of a carboxyl group, a hydroxyl group, and a sulfonic acid group.

5. The negative electrode material according to claim 4, characterized in that The diamine residue with a polar functional group is derived from at least one of the following diamine monomer compounds containing polar groups: 3,5-diaminocyclohexanecarboxylic acid, 3,5-diaminobenzoic acid, 4,4'-diaminobiphenyl-2,2'-dicarboxylic acid, 5,5'-methylenebis(2-aminobenzoic acid), 3,3'-dihydroxybenzidine, 2,2'-bis(3-amino-4-hydroxyphenyl)propane, 2,2'-bis(3-amino-4-hydroxyphenyl)hexafluoropropane, bis(3-amino-4-hydroxyphenyl)sulfone, 4,6-diaminoresorcinol dihydrochloride, 2,5-diamino-1,4-benzenedithiol dihydrochloride, 2,6-dihydroxy-3,7-diaminotriphenylene, 2,2'-bis[3-(4-aminobenzamido)-4-hydroxyphenyl]hexafluoropropane, 4,4'-diamino-2,2'-biphenyldisulfonic acid, 4,4'-diaminostilbene-2,2'-disulfonic acid.

6. The negative electrode material according to claim 1, characterized in that The preparation method of the polymer includes: Under an inert atmosphere and the action of a catalyst, subjecting a dianhydride monomer, a diamine monomer containing an alicyclic ring, and an optional diamine monomer containing a polar group to a polymerization reaction in a first solvent to obtain the polymer; The catalyst includes at least one of isoquinoline, triethylamine, benzoic acid, and p-hydroxybenzoic acid.

7. The negative electrode material according to claim 6, characterized in that The subjecting a dianhydride monomer, a diamine monomer containing an alicyclic ring, and an optional diamine monomer containing a polar group to a polymerization reaction under an inert atmosphere and the action of a catalyst includes: Mixing the dianhydride monomer, the diamine monomer containing an alicyclic ring, and the optional diamine monomer containing a polar group with the first solvent uniformly to obtain a first mixed solution; Mixing the first mixed solution with the catalyst uniformly at 75°C - 90°C to obtain a second mixed solution; Subjecting the second mixed solution to the polymerization reaction at 160°C - 200°C to obtain a reaction product solution containing the polymer; Performing a separation treatment on the reaction product solution containing the polymer to obtain the polymer.

8. The negative electrode material according to claim 1, characterized in that The active material further includes a carbon-based negative electrode material; The weight percentage of the silicon-based negative electrode material in the active material is 1wt% - 99.5wt%.

9. The negative electrode material according to claim 8, characterized in that The silicon-based negative electrode material includes at least one of silicon, silicon oxide material, and silicon carbon material; The carbon-based negative electrode material includes at least one of graphite, hard carbon, and soft carbon.

10. The negative electrode material according to any one of claims 1 to 9, characterized in that The weight percentage of the binder in the negative electrode material is 1wt% - 20wt%; The weight percentage of the conductive agent in the negative electrode material is 1wt% - 20wt%; The active material is the balance.

11. A negative electrode plate, characterized in that: The negative electrode plate comprises: an active material layer and a current collector, wherein the active material layer is located on at least one surface of the current collector; The active material layer is prepared by using the negative electrode material according to any one of claims 1 to 10.

12. The negative electrode sheet according to claim 11, characterized in that: The current collector includes at least one of copper foil, copper mesh, carbon-coated copper foil, stainless steel foil, stainless steel mesh, carbon-coated stainless steel foil, and nickel foil.

13. A lithium ion battery, characterized in that: The lithium-ion battery comprises the negative electrode sheet according to any one of claims 11 to 12.

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